The quest to develop larger and larger semiconductors of the dynamic random access memory (DRAM) type is a well known goal. The industry has steadily progressed from DRAMs of the 16K type, shown in U.S. Pat. No. 4,081,701 issued to White, McAdams and Redwine, and the 64K type, shown in U.S. Pat. No. 4,055,444 issued to Rao, to DRAMs of the 1M type, as described in U.S. Pat. No. 4,658,377 issued to McElroy. DRAMs of the 4M type are now being produced. Production plans for 16M DRAMs of submicron technology now exist and experimentation of 64M DRAMs has begun. One factor furthering the development of larger DRAMs is the reduction in memory cell geometries as illustrated in U.S. Pat. No. 4,240,092 to Kuo (a planar capacitor cell), and as illustrated in U.S. Pat. No. 4,721,987 to Baglee et al. (a trench capacitor cell). The trench capacitor cell of Baglee describes it's upper plate as a polysilicon layer extending into the trench. This polysilicon layer extends over the face of the silicon bar to form field plate isolation over the face of the bar.
In developing submicron 16MB DRAMs of the trench capacitor type having field plate isolation, process engineers have encountered a potential shorting problem caused by undesirable polysilicon gate, poly si, filaments. During processing, these poly si filaments sometimes can remain around the field plate openings. The polysilicon word lines, that also act as the gate electrodes for the pass gate transistors, lie in close proximity to the edge of the field plate openings. The poly si filaments can extend into the polysilicon word lines and thereby cause shorting between adjacent polysilicon gate electrodes. Another undesirable effect of poly si filaments is a contribution to low gate breakdown voltages.
It is the object of this invention to provide a method to eliminate undesirable polysilicon gate filaments on field plate isolated devices such as high density dynamic random access memories.
Other objects and advantages of the invention will be apparent to those of ordinary skill in the art having reference to the following specification, together with the drawings.